<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" >
<head>
  <title>文字提示效果</title>
  <style type="text/css">
    *{
      margin:0px;padding:0px;font-size:12px;
    }
    input{
      width:100px;height:20px;border:1px solid #ccc;
    }
  </style>
</head>
<body>
<script language="javascript">
  function tips(id,str){
    var l=document.getElementById(id).offsetLeft+120;
    var t=document.getElementById(id).offsetTop;
    document.getElementById("tips").innerHTML="提示："+str;
    document.getElementById("tips").style.left=l+"px";
    document.getElementById("tips").style.top=t+"px";
    document.getElementById("tips").style.display="";
  }
  function outtips(){
    document.getElementById("tips").style.display='none';
  }
</script>
<div id="tips" style="position:absolute;border:1px solid #ccc;padding:0px 3px;color:#f00;display:none;height:20px;line-height:20px;background:#fcfcfc"></div>
<br />
姓名：<input type="text" id="username" onfocus="tips('username','姓名长度最多16个字符')" onblur="outtips()" />
<br />
密码：<input type="password" id="password" onfocus="tips('password','密码长度必须在3-18位之间')" onblur="outtips()">